The invention relates to a contact element for press fitting into a hole of a printed circuit board having a hole for receiving a contact element.
The press fitting technique is a method to connected electrical contacts with printed circuit boards without using soldering. The press-fit contact has a deformable (flexible) or solid press-fit zone. The press-fit zone is oversized in relation to the corresponding bore hole in the PCB, which is coated with copper. The electrical contact between the press-fit pin and the PCB is produced by press fitting the pin with a mechanical force into the bushing, i.e. no solder or other auxiliary aids are used. The normal force required to maintain a stable and reliable connection is created by the elastic deformation of the press-fit zone (flexible pin) and the PCB (solid pin). In addition, the high mechanical pressure in the press-fit zone leads to cold welding.
With the flexible press fitting technique, the press-fit zone comprises an elastic deformable region. The deformation of the press-fit zone when press-fit causes a normal force to be applied to the surrounding copper bushing, which determines the retention force of the pin in the bushing. The most simple possible development of an elastic press-fit zone is the so-called Needle Eye Zone in the form of a needle eye. In the Needle Eye Zone, the press-fit limbs comprise on the outside a continuous concave curve. This geometry results in a very uneven force distribution over the length of the press-fit zone when press-fit. High force levels occur in a narrowly restricted area in the centre of the press-fit zone, while above and below, increased forces hardly occur, and the press-fit limbs are not in contact with the bushing over a wide area.
If the outer sides of the limbs are designed to be parallel in the deformable region, stress peaks occur on the edges of the deformable region, and low stress occurs in the centre, and the limbs may even bend inwardly in the centre.
A modified Needle Eye Zone is known from the First Publication DE 197 26 759 A1. This zone comprises a modified inner contour, which is intended to create a more even distribution of force during press-fitting.
Contact elements with flexible press-fit zones are known from EP 0 148 792 or EP 0 367 866 or U.S. Pat. No. 5,564,954, in which catches which face each other inwardly are formed on each of the limbs, which restrict the deformation of the limbs transverse to the direction of insertion accordingly, and which apply a corresponding counterforce onto the limbs during further compression. Here, the counterforce is initially very low, depending on the degree of compression of the limbs, and increases rapidly when the catches come into contact with each other. For a defined specification of the press-fit forces, therefore, a precise correlation is required between the diameter of the hole and the outer dimension of the limb and the inner dimension of the catch, and low-level deviations already lead to significant deviations in the press-fit forces achieved.
In addition, a contact element is already known from the category-defining DE 19934709, in which the deformable region comprises a front and a rear region, and the two regions each have a closed opening, which are separated by a crossbar which runs transverse to the insertion direction of the contact element, i.e. the limbs of these press-fit zones are separated by the openings, yet connected with each other by the crossbar. The contact element comprises a constriction in the region of the crossbar, however, and is smaller in the front region, as a result of which the outer edges of the limbs which lie on the edge of the hole also fail to touch the hole over a sufficiently wide area, leading to uneven stress with a too high level of local fluctuation. The crossbar runs vertically to the insertion direction and is hardly able to have a springy elastic effect.
The object of the invention is therefore to provide a contact element which enables the safest and most even affixation and contacting in the opening of the printed circuit board. This object is achieved by a contact element for pressing into a hole of a printed circuit board. The contact element comprises a rod-shaped press-fit zone with an insertion region and an adjacent deformable region, and the deformable region has a width (D1) which is larger than the diameter of the hole. The insertion region has a width (D2) which is smaller than the diameter of the hole and the deformable region comprises at least two limbs (4, 4a) and in the insertion direction (F) a front (1) and a rear region (2), both of which having a closed opening, which are separated by a crossbar (3). The crossbar is curved in the form of a wave in the insertion direction (F), and runs at least in a partial section with a pointed angle (α) between 5 and 85 degrees to the insertion direction (F).